Stator assembly

ABSTRACT

A high speed spindle motor is constructed from a stator assembly that includes a stator having multiple conductors that create a plurality of magnetic fields when electrical current is conducted by the conductors and a body of a phase change material, such as a thermoplastic, substantially encapsulating the stator. A rotatable hub having a magnet connected thereto is in operable proximity to the stator. The high speed motor also includes a shaft, a bearing surrounding the shaft and one of the bearing or shaft being fixed to the stator assembly and the other of the bearing or shaft being fixed to the rotatable hub. Hard disc drives using the motor, and methods of developing and constructing the motor and hard disc drives are also disclosed.

REFERENCE TO EARLIER FILED APPLICATION

The present application claims the benefit of the filing date under 35U.S.C. §119(e) of provisional U.S. patent application Ser. No.60/146,446, filed Jul. 29, 1999, which is hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates generally to a high speed motor. Itrelates particularly to a spindle motor such as used in a hard discdrive, and to the construction and arrangement of the body of thespindle motor to align and retain the respective component parts of themotor, as well as stator assemblies used in the motors and hard discdrives using the motors, and methods of developing and manufacturinghigh speed motors.

BACKGROUND OF THE INVENTION

Computers commonly use disc drives for memory storage purposes. Discdrives include a stack of one or more magnetic discs that rotate and areaccessed using a head or read-write transducer. Typically, a high speedmotor such as a spindle motor is used to rotate the discs.

An example of a conventional spindle motor 1 is shown in FIG. 1. Themotor 1 includes a base 2 which is usually made from die cast aluminum,a stator 4, a shaft 6, bearings 7 and a disc support member 8, alsoreferred to as a hub. A magnet 3 and flux return ring 5 are attached tothe disc support member 8. The stator 4 is separated from the base 2using an insulator (not shown) and attached to the base 2 using a glue.Distinct structures are formed in the base 2 and the disc support member8 to accommodate the bearings 7. One end of the shaft 6 is inserted intothe bearing 7 positioned in the base 2 and the other end of the shaft 6is placed in the bearing 7 located in the hub 8. A separate electricalconnector 9 may also be inserted into the base 2.

Each of these parts must be fixed at predefined tolerances with respectto one another. Accuracy in these tolerances can significantly enhancemotor performance.

In operation, the disc stack is placed upon the hub. The stator windingsare selectively energized and interact with the permanent magnet tocause a defined rotation of the hub. As hub 8 rotates, the head engagesin reading or writing activities based upon instructions from the CPU inthe computer.

Manufacturers of disc drives are constantly seeking to improve the speedwith which data can be accessed. To an extent, this speed depends uponthe speed of the spindle motor, as existing magneto-resistive headtechnology is capable of accessing data at a rate greater than the speedoffered by the highest speed spindle motor currently in production. Thespeed of the spindle motor is dependent upon the dimensional consistencyor tolerances between the various components of the motor. Greaterdimensional consistency between components leads to a smaller gapbetween the stator 4 and the magnet 3, producing more force, whichprovides more torque and enables faster acceleration and higherrotational speeds. One drawback of conventional spindle motors is that anumber of separate parts are required to fix motor components to oneanother. This can lead to stack up tolerances which reduce the overalldimensional consistency between the components. Stack up tolerancesrefers to the sum of the variation of all the tolerances of all theparts, as well as the overall tolerance that relates to the alignment ofthe parts relative to one another.

In an effort to enable increased motor speed, some hard discmanufacturers have turned to the use of hydrodynamic bearings. Thesehydrodynamic bearings, however, have different aspect ratios fromconventional bearings. An example of a different aspect ratio may befound in a cylindrical hydrodynamic bearing in which the length of thebearing is greater than it's diameter. This results in moresusceptibility to problems induced by differing coefficients of thermalexpansion than other metals used in existing spindle motors, making itdifficult to maintain dimensional consistency over the operatingtemperature that the drive sees between the hydrodynamic bearings andother metal parts of the motor. Hydrodynamic bearings have lessstiffness than conventional ball bearings so they are more susceptibleto imprecise rotation when exposed to vibrations or shock.

An important characteristic of a hard drive is the amount of informationthat can be stored on a disc. One method to store more information on adisc is to place data tracks more closely together. Presently thisspacing between portions of information is limited due to vibrationsoccurring during the operation of the motor. These vibrations can becaused when the stator windings are energized, which results invibrations of a particular frequency. These vibrations also occur fromharmonic oscillations in the hub and discs during rotation, causedprimarily by non-uniform size media discs.

An important factor in motor design is the lowering of the operatingtemperature of the motor. Increased motor temperature affects theelectrical efficiency of the motor and bearing life. As temperatureincreases, resistive loses in wire increase, thereby reducing totalmotor power. Furthermore, the Arhennius equation predicts that thefailure rate of an electrical device is exponentially related to itsoperating temperature. The frictional heat generated by bearingsincreases with speed. Also, as bearings get hot they expand, and thebearing cages get stressed and may deflect, causing non-uniform rotationand the resultant further heat increase, non-uniform rotation requiringgreater spacing in data tracks, and reduced bearing life. One drawbackwith existing motor designs is their limited effective dissipation ofthe heat, and difficulty in incorporating heat sinks to aid in heatdissipation. In addition, in current motors the operating temperaturesgenerally increase as the size of the motor is decreased.

Manufacturers have established strict requirements on the outgassing ofmaterials that are used inside a hard disc drive. These requirements areintended to reduce the emission of materials onto the magnetic media orheads during the operation of the drive. Of primary concern are gluesused to attach components together, varnish used to insulate wire, andepoxy used to protect steel laminations from oxidation.

In addition to such outgassed materials, airborne particulate in a drivemay lead to head damage. Also, airborne particulates in the disc drivecould interfere with signal transfer between the read/write head and themedia. To reduce the effects of potential airborne particulate, harddrives are manufactured to exacting clean room standards and air filtersare installed inside of the drive to reduce the contamination levelsduring operation.

Heads used in disc drives are susceptible to damage from electricalshorts passing through a small air gap between the media and the headsurface. In order to prevent such shorts, some hard drives use a plasticor rubber ring to isolate the spindle motor from the hard drive case. Adrawback to this design is the requirement of an extra component.

Another example of a spindle motor is shown in U.S. Pat. No. 5,694,268(Dunfield et al.) (incorporated herein by reference). Referring to FIGS.7 and 8 of this patent, a stator 200 of the spindle motor isencapsulated with an overmold 209. The overmolded stator containsopenings through which mounting pins 242 may be inserted for attachingthe stator 200 to a base. U.S. Pat. No. 5,672,972 (Viskochil)(incorporated herein by reference) also discloses a spindle motor havingan overmolded stator. One drawback with the overmold used in thesepatents is that it has a different coefficient of linear thermalexpansion (“CLTE”) than the corresponding metal parts to which it isattached. Another drawback with the overmold is that it is not veryeffective at dissipating heat. Further, the overmolds shown in thesepatents are not effective in dampening some vibrations generated byenergizing the stator windings.

U.S. Pat. No. 5,806,169 (Trago) (incorporated herein by reference)discloses a method of fabricating an injection molded motor assembly.However, the motor disclosed in Trago is a step motor, not a high speedspindle motor, and would not be used in applications such as hard discdrives. Thus, a need exists for an improved high speed spindle motor,having properties that will be especially useful in a hard disc drive,overcoming the aforementioned problems.

BRIEF SUMMARY OF THE INVENTION

A high speed motor has been invented which overcomes many of theforegoing problems. In addition, unique stator assemblies and othercomponents of a high speed motor have been invented, as well as methodsof manufacturing and developing motors and hard disc drives. In oneaspect, the invention is a high speed spindle motor comprising: a statorassembly, including a stator having multiple conductors that create aplurality of magnetic fields when electrical current is conducted by theconductors; and a body of a phase change material substantiallyencapsulating the stator; a rotatable hub having a magnet connectedthereto in operable proximity to the stator; a shaft; a bearing aroundthe shaft; and one of the shaft or bearing being fixed to the statorassembly and the other of the shaft or bearing being fixed to therotatable hub.

In another aspect the invention is a stator assembly comprising a) amagnetically inducible core; b) a plurality of conductors in proximityto the core such that magnetic fields are induced in the core whenelectrical current is conducted through the conductors; and c) a body ofa phase change material substantially encapsulating the core andconductors, the phase change material having a coefficient of linearthermal expansion approximately the same as the coefficient of linearthermal expansion of the core.

In another aspect the invention is a stator assembly comprising: a) astator having multiple conductors that create a plurality of magneticfields when electrical current is conducted through the conductors; andb) a body of phase change material substantially encapsulating theconductors, the phase change material having a thermal conductivity ofat least 0.7 watts/meter° K. and a dielectric strength of at least 250volts/mil.

The invention provides the foregoing and other features, and theadvantages of the invention will become further apparent from thefollowing detailed description of the presently preferred embodiments,read in conjunction with the accompanying drawings. The detaileddescription and drawings are merely illustrative of the invention and donot limit the scope of the invention, which is defined by the appendedclaims and equivalents thereof.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an exploded, partial cross-sectional and perspective view of aprior art high speed motor.

FIG. 2 is a perspective view of a stator used in a first embodiment ofthe present invention.

FIG. 3 is an exploded, partial cross-sectional and perspective view of ahigh speed motor in accordance with the first embodiment of the presentinvention.

FIG. 4 is a cross-sectional view of the high speed motor of FIG. 3.

FIG. 5 is an exploded, partial cross-sectional and perspective view of ahigh speed motor in accordance with a second embodiment of the presentinvention.

FIG. 6 is a cross-sectional view of the high speed motor shown in FIG.5.

FIG. 7 is an exploded, partial cross-sectional and perspective view of ahigh speed motor in accordance with a third embodiment of the presentinvention.

FIG. 8 is an exploded, partial cross-sectional and perspective view of ahigh speed motor in accordance with a fourth embodiment of the presentinvention.

FIG. 9 is a cross-sectional view of a high speed motor in accordancewith a fifth embodiment of the present invention.

FIG. 10 is a cross-sectional view of a high speed motor in accordancewith a sixth embodiment of the present invention.

FIG. 11 is a cross-sectional view of a high speed motor in accordancewith a seventh embodiment of the present invention.

FIG. 12 is a perspective view of the inserts used in the high speedmotor of FIG. 11.

FIG. 13 is a cross-sectional view of a high speed motor in accordancewith an eighth embodiment of the present invention.

FIG. 14 is an exploded, partial cross-sectional and perspective view ofa high speed motor in accordance with the ninth embodiment of thepresent invention.

FIG. 15 is a drawing of a mold used to make the encapsulated stator ofFIG. 3.

FIG. 16 is a drawing of the mold of FIG. 15 in a closed position.

FIG. 17 is an exploded and partial cross sectional view of componentsused in a pancake motor, a tenth embodiment of the invention.

FIG. 18 is a cross-sectional view of a high speed motor in accordancewith an eleventh embodiment of the invention.

FIG. 19 is a perspective view of a stator and shaft used in a twelfthembodiment of the present invention.

FIG. 20 is an exploded and partial cross sectional view of a hard discdrive of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS AND PREFERRED EMBODIMENTS OF THEINVENTION First Embodiment

A first embodiment of a high speed motor of the present invention isshown in FIGS. 2-4. By “high speed” it is meant that the motor canoperate at over 5,000 rpm. The spindle motor 10 is designed for rotatinga disc or stack of discs in a computer hard disc drive. Motor 10 isformed using an encapsulation method which reduces the number of partsneeded to manufacture the motor as compared with conventional motorsused for disc drives, thereby reducing stack up tolerances andmanufacturing costs and producing other advantages discussed below.

Referring to FIG. 2, a stator 20 is first constructed, usingconventional steel laminations 11 forming a magnetically inducible core17 having a plurality of salient poles 21 thereon, and wire windings 15which serve as conductors. The conductors induce or otherwise create aplurality of magnetic fields in the core when electrical current isconducted through the conductors. In this embodiment, a magnetic fieldis induced in each of the poles 21.

The stator 20 is then used to construct the rest of the spindle motor 10(FIG. 3). The spindle motor 10 includes a hub 12, which serves as a discsupport member, the stator 20 and a body 14. Together the stator 20 andbody 14 make up a stator assembly 13. The body 14 is preferably amonolithic body 14. Monolithic is defined as being formed as a singlepiece. The body 14 substantially encapsulates the stator 20. Substantialencapsulation means that the body 14 either entirely surrounds thestator 20, or surrounds almost all of it except for minor areas of thestator that may be exposed. However, substantial encapsulation meansthat the body 14 and stator 20 are rigidly fixed together, and behave asa single component with respect to harmonic oscillation vibration.

The body 14 is preferably formed of a phase change material, meaning amaterial that can be used in a liquid phase to envelope the stator, butwhich later changes to a solid phase. There are two types of phasechange materials that will be most useful in practicing the invention:temperature activated and chemically activated. A temperature activatedphase change material will become molten at a higher temperature, andthen solidify at a lower temperature. However, in order to be practical,the phase change material must be molten at a temperature that is lowenough that it can be used to encapsulate a stator. Preferredtemperature activated phase change materials will be changed from aliquid to a solid at a temperature in the range of about 200 to 700° F.The most preferred temperature activated phase change materials arethermoplastics. The preferred thermoplastic will become molten at atemperature at which it is injection-moldable, and then will be solid atnormal operating temperatures for the motor. An example of a phasechange material that changes phases due to a chemical reaction, andwhich could be used to form the body 14, is an epoxy. Other suitablephase change materials may be classified as thermosetting materials.

As shown in FIG. 4, a shaft 16 is connected to the hub or disc supportmember 12 and is surrounded by bearings 18, which are adjacent againstthe body 14. A rotor or magnet 28 is fixed to the inside of the hub 12on a flange so as to be in operable proximity to the stator. The magnet28 is preferably a permanent magnet, as described below. The body 14includes a base 22. In addition, mounting features, such as apertures25, and terminals comprising a connector 26 for connecting theconductors to an external power source are formed as a part of thestator assembly. The terminals 26 are partially encapsulated in the body14.

Referring to FIGS. 3-4, the base 22 of the body 14 is generallyconnected to the hard drive case (not shown). Connecting members (notshown), such as screws, may be used to fix the base 22 to the hard drivecase, using holes 25 as shown in FIG. 3. Alternatively, other types ofmounting features such as connecting pins or legs may be formed as partof the base 22. The connector 26 is preferably a through-hole pin typeof connector 26 and is coupled through the hard drive case to thecontrol circuit board residing on the outer surface of the base (notshown). Alternatively the connector may be a flexible circuit withcopper pads allowing spring contact interconnection.

The stator 20 is positioned in the body 14 generally in a directionperpendicular to an interior portion 30. Referring to FIG. 2, the stator20 is preferably annular in shape and contains an open central portion32. The poles 21 extend radially outward from this central portion 32.Faces of the poles 21 are positioned outward relative to the centralportion 32 of the stator 20. The body 14 is molded around the stator 20in a manner such that the faces of the poles are exposed and aresurrounded by and aligned concentrically with respect to the discsupport member 12. Alternatively, the poles may be totally encapsulatedin body 14 and not be exposed.

Referring to FIG. 4, the body 14 has an upper portion 40 that extendsupwardly from the stator 20. The upper portion 40 is also preferablyannular shaped. The body 14 includes the interior portion 30. Theinterior portion 30 is generally sized and shaped to accommodate thebearings 18. The interior portion 30 includes an upper support portion42 and a lower support portion 44. In the embodiment illustrated in FIG.4 the interior portion 30 is preferably cylindrically shaped.

The phase change material used to make the body 14 is preferably athermally conductive but non-electrically conductive plastic. Inaddition, the plastic preferably includes ceramic filler particles thatenhance the thermal conductivity of the plastic. A preferred form ofplastic is polyphenyl sulfide (PPS) sold under the tradename “Konduit”by LNP. Grade OTF-212 PPS is particularly preferred. Examples of othersuitable thermoplastic resins include, but are not limited to,thermoplastic resins such as 6,6-polyamide, 6-polyamide, 4,6-polyamide,12,12-polyamide, 6,12-polyamide, and polyamides containing aromaticmonomers, polybutylene terephthalate, polyethylene terephthalate,polyethylene napththalate, polybutylene napththalate, aromaticpolyesters, liquid crystal polymers, polycyclohexane dimethylolterephthalate, copolyetheresters, polyphenylene sulfide, polyacylics,polypropylene, polyethylene, polyacetals, polymethylpentene,polyetherimides, polycarbonate, polysulfone, polyethersulfone,polyphenylene oxide, polystyrene, styrene copolymer, mixtures and graftcopolymers of styrene and rubber, and glass reinforced or impactmodified versions of such resins. Blends of these resins such aspolyphenylene oxide and polyamide blends, and polycarbonate andpolybutylene terephthalate, may also be used in this invention.

Referring to FIG. 4, the bearings 18 include an upper bearing 46 and alower bearing 48. Also, each bearing 18 has an outer surface 50 and aninner surface 52. The outer surface 50 of the upper bearing contacts theupper support portion 42 and the outer surface 50 of the lower bearing48 contacts the lower support portion 44. The inner surfaces 52 of thebearings 18 contact the shaft 16. The bearings are preferably annularshaped. The inner surfaces 52 of the bearings 18 may be press fit ontothe shaft 16. A glue may also be used. The outer surface 50 of thebearings 18 may be press fit into the interior portion 30 of the body14. A glue may also be used. The bearings in the embodiment shown inFIGS. 3-4 are ball bearings. Alternatively other types of bearings, suchas hydrodynamic or combinations of hydrodynamic and magnetic bearings,may be used. The bearings are typically made of stainless steel.

The shaft 16 is concentrically disposed within the interior portion 30of the body 14. The bearings 18 surround portions of the shaft 16. Asdescribed above, the inner surfaces 52 of the bearings are in contactwith the shaft 16. The shaft 16 includes a top portion 54 and a bottomportion 56. The top portion 54 of the shaft 16 is fixed to the hub 12.The bottom portion 54 of the shaft 16 is free to rotate inside the lowerbearing. Thus, in this embodiment, the shaft 16 is freely rotatablerelative to the body 14. The shaft 16 is preferably cylindrical shaped.The shaft 16 may be made of stainless steel.

Referring to FIG. 4, the hub 12 is concentrically disposed around thebody 14. The hub 12 is fixed to the shaft 16 and is spaced apart fromthe body 14. The hub 12 includes a flux return ring 58 and the magnet28. The flux return ring 58 is glued to the disc support member. Themagnet 28 is glued to the hub 12. As shown in FIG. 4, the magnet 28concentrically surrounds the portion of the body 14 that includes thestator 20. In this embodiment the magnet 28 and stator 20 are generallycoplanar when the motor 10 is assembled.

The magnet 28 is preferably a sintered part and is one solid piece. Themagnet 28 is placed in a magnetizer which puts a plurality of discreteNorth and South poles onto the magnet 28, dependant on the number ofpoles 21 on the stator 20. The flux return ring 58 is preferably made ofa magnetic steel. The hub is preferably made of aluminum. Also, the hubmay be made of a magnetic material to replace the flux return ring.

Operation of the First Embodiment

In operation, the spindle motor shown in FIGS. 3-4 is driven bysupplying electrical pulses to the connector 26. These pulses are usedto selectively energize the windings 15 around the stator 20 poles 21.This results in a moving magnetic field. This magnetic field interactswith the magnetic field generated by the magnet 28 in a manner thatcauses the magnet 28 to rotate about the body 14. As a result, the hub12 begins to rotate along with the shaft 16. The bearings 18 facilitatethe rotation of the shaft 16.

Discs or a disc stack (not shown) that are placed upon hub are caused torotate as the hub 12 rotates. A head (not shown) then reads and writesdata to and from the discs.

Method of Making the First Embodiment

The spindle motor 10 shown in FIGS. 3 and 4 is made in part using anencapsulation technique. This encapsulation technique involves thefollowing steps, and uses the mold shown in FIGS. 15 and 16. First, amold is constructed to produce a part with desired geometry. The moldhas two halves 72 and 74. Also, core pins 76 are connected to a plate 78that is activated by hydraulic cylinders 77 within the mold tool. Thestator 20 is placed within the mold and the two halves are closed. Thecore pins hold the stator 20 in its correct position. Second, usingsolid state process controlled injection molding, plastic is injectedthrough gate 80 around the stator, so as to encapsulate the stator andform the body 14 shaped as shown in FIGS. 3 and 4. As plastic flows in,pins 76 are withdrawn so that the plastic completely surrounds thestator.

After the stator assembly is formed, the shaft 16 is press fit andpossibly glued into the bearings. Next, glue is placed on the outerbearing surfaces and the bearings and shaft are press fit into theinterior portion 30 of the plastic body 14. It may be desirable to moldthe interior portion 30 smaller than necessary and drill it out afterthe molding step to fit the exact size of the bearings being used. Nextthe aluminum disc support member 12 is machined and the magnet and fluxreturn ring are glued onto the lower surfaces. The disc support member12 is then glued to the motor shaft.

After the spindle motor and hub are assembled they can be used toconstruct a hard disc drive by using the holes 25 to mount the motor tothe base of the hard disc drive. Thereafter, construction of the harddisc drive can follow conventional methods.

Advantages of the First Embodiment

An advantageous feature of the first embodiment is provided by the factthat the body 14 is preferably a monolithic body 14 or monolithicallyformed using an encapsulation technique. This monolithic body 14provides a single structure that aligns the stator, bearings, shaft anddisc support member relative to one another. (Further this single pieceprovides support for the bearings and a base 22 that allows connectionto a hard disc drive). The use of multiple parts in previous devicesresults in stack up tolerances and increased manufacturing costs.Conversely, the single unitized body of the present invention providesalignment for the components of a spindle motor and couples thesecomponents to one another. By encapsulating the body 14, and therebymolding some components as part of the body 14 and using the body toalign the remaining components, stack up tolerances are substantiallyreduced, along with manufacturing costs. This also leads to greatermotor efficiency and performance.

The disclosed spindle motor optimizes dimensional tolerances among motorcomponents and thereby enables higher rotational speeds. The fact thatthe preferred body is made of thermoplastic allows the use of a type ofthermoplastic with a CLTE similar to that of the steel bearing cases.This in turn facilitates optimal interference fits between bearings,such as hydrodynamic bearings and the motor body. In the past, suchinterference fits where difficult to achieve because of the differencein thermal expansion coefficients of the bearings and the componentparts of the motor. As the motor heats up, and the bearings get hot, thebearing cases are put under stress as they try to expand. The bearingcases can even deflect, resulting in non-uniform rotation. This limitedhow close the data tracks could be spaced together.

Further, to prevent the motor from seizing when it got hot, larger thandesired gaps between the magnet 28 and the stator 20 were used so thatwhen pieces expanded from being heated, the magnet would not contact thestator. If the magnet contacted the stator, the contact would generatemagnetic particulate which can damage the heads and interfere with theirability to read or record data on the discs. Also, if the body has aCLTE greater than that of the steel lamination in the stator, the gaphas to be large enough so that the expansion of the body as the motorheats up does not cause the body to contact the rotating magnet (eventhough the steel laminations are not close to contacting the magnet).With the preferred embodiment of the present invention, with the CLTE ofthe body matching that of the steel laminations, much smaller gaps, aslow as 0.005 inches and more preferably as low as 0.003 inches, can beutilized. As the body expands, it only expands at the same rate as thelaminations, and does not grow to the point that the body diminishes thegap size to zero. Thus, the only gap that is needed is one sufficientfor expansion of the steel laminations. These smaller gaps make themotor more efficient, as the electrical efficiency of the motordecreases with larger distances between the stator and the rotatingmagnet.

Through the use of the present embodiment, a particular plastic may bechosen for the body 14 that has properties of rockwell hardness, flexmodulus, and elongation that are specifically designed to counteract thevibratory frequencies generated by the motor. Thus, the disclosedspindle motor substantially reduces motor vibration. This reducedvibration allows information on a disc to be stored closer together,thereby enabling higher data density.

As discussed above, controlling heat dissipation in conventional spindlemotors is difficult to achieve. A particular plastic may be chosen forencapsulating the body 14 that is designed to facilitate heatdissipation. By putting this material in intimate contact with the twoheat sources (motor windings and bearing) and then creating a solidthermal conductive pathway to the housing of the drive, overall motortemperature may be reduced. Moreover, heat sinks may be convenientlyencapsulated within the body 14 during the molding process. These heatsinks may consist of metal inserts, which arc discussed in greaterdetail below. The fact that these inserts are encapsulated within thebody, as opposed to being separately attached, simplifies themanufacturing process and allows for post machining to enable moreprecise tolerances and ensures that dimensional consistency will bemaintained over the motors life.

The disclosed spindle motor also reduces the emission of materials fromthe motor components onto the magnetic media or heads of the disc drive.This is achieved because components such as the stator, whichpotentially emit such materials, are substantially encapsulated inplastic. Further materials such as glue used to attach componentstogether are eliminated through the use of a monolithic body 14.

In addition, the disclosed spindle motor obviates the necessity of aseparate plastic or rubber ring sometimes used to isolate the spindlemotor from the hard drive in order to prevent shorts from beingtransferred to the magnetic media and ultimately the read-write heads.Because the disclosed spindle motor body 14 is preferably made of anon-electrically conductive (having a dielectric strength of at least250 volts/mil) and injectable thermoplastic material, such a separaterubber isolating ring is unnecessary. Once again this reducesmanufacturing costs and the stack up tolerances associated with using anadditional part.

Second Embodiment

Referring to FIGS. 5-6, a second embodiment of the spindle motor 110 isshown. This embodiment is similar to the embodiment shown in FIGS. 2-4and like components are labeled with similar reference numerals with anaddend of 100. A monolithic body 114 is formed by an encapsulationmethod. The primary difference between the first embodiment and thesecond embodiment is that in the second embodiment, the magnet 128 isconcentrically surrounded by the stator 120 when the motor 110 isassembled, as opposed to the first embodiment where the stator 20surrounds the magnet 28. Also, in order to achieve this positioning, thebody 114 is shaped differently. Referring to FIG. 6, the body 114 isshaped such that the portion of the body 114 containing the stator 120concentrically surrounds the portion of the body surrounding the shaft116, and a gap 160 is formed between these two portions. The poles onthe core are salient poles, but are directed inwardly. Further, inaccordance with this positioning, the magnet 128 is positioned on anouter portion of the hub and the flux return ring 158 is positionedinterior to the magnet 128.

In the embodiment shown in FIGS. 5-6 a hydrodynamic bearing 118 is used.Hydrodynamic bearings can be an air bearings. The fluid used inhydrodynamic bearings can be either a liquid or gas. The bearing 118concentrically surrounds a substantial portion of the shaft.Alternatively, ball bearings such as the ones shown in the firstembodiment could be used in the second embodiment. Finally, in thesecond embodiment the inner portion 130 of the body 114 does not extendthrough the entire length of the body 114, although in an alternateembodiment it could. The second embodiment may be made and used in asimilar manner as the first embodiment. This embodiment has theadvantages discussed above in conjunction with the first embodiment. Theuse of a hydrodynamic bearing is possible because there is less stresson the bearing case, as well as the fact that this motor is easier toassemble. The use of a hydrodynamic bearings provides less friction,less wear resistance and hence a longer bearing life, less vibration andthe capability to operate at higher speeds.

Third Embodiment

Referring to FIG. 7 a third embodiment of a spindle motor is shown. Thisembodiment is similar to the embodiment shown in FIGS. 5-6 and likecomponents are labeled with similar numerals with an addend of 200. Amonolithic body 214 is formed by an encapsulation method. In the thirdembodiment, the hub 212 is made of steel so that the flux return ring258, which must be of a material that will propagate magnetic energy,can be made as an extension of the rest of the hub. The magnet 228 isfixed to the flux return ring 258.

The third embodiment demonstrates the use of inserts. In general, theterm “insert” is used to describe any component other than the elementsof the stator that are substantially encapsulated in the phase changematerial with the stator. Different inserts may be used to providedifferent benefits. The inserts may be used to provide structuralrigidity, thermal conductivity, vibration dampening or enhanced magneticeffect. The inserts may themselves be magnetic. These second magnets canbe enhancement magnets, which are directly involved with theelectromechanical functioning of the motor, or can be parts of amagnetic bearing (described in more detail below). The inserts mayenhance heat transfer away from the bearing and stator. The inserts mayenhance dampening of motor vibration. This may reduce audible noise aswell as improve motor life and allow for closer data track spacing.

In the embodiment of FIG. 7, there are two inserts. Specifically, acentral insert 260 is molded within the upper portion 240 of the body214. The central insert 260 is molded concentrically with respect to theupper portion 240. A base insert 262 is molded within the base 222portion of the body 214. The central insert 260 and the base insert 262serve to enhance the stiffness of the body 214. These inserts alsoimprove the overall thermal conductivity of the body 214, and therebyimprove motor performance. The inserts may also be used in combinationwith the encapsulant to dampen unwanted vibrations or audible noise. Theplastic body 214 locks the inserts into position with a high degree ofstrength. These inserts may be entirely overmolded by plastic oralternatively portions of these inserts may be exposed. The thirdembodiment may be made and used in a similar manner as the firstembodiment. This embodiment has the advantages discussed above inconjunction with the first embodiment, as well as the advantage from theuse of inserts 260 and 262.

Fourth Embodiment

A fourth embodiment of the spindle motor is shown in FIG. 8. The spindlemotor 310 includes components that are similar to the previousembodiments, in particular the second embodiment, shown in FIGS. 5-6. Amonolithic body 314 is formed using an encapsulation method. The primarydifference between the fourth embodiment and the second embodiment isthat the fourth embodiment includes magnetic bearings, one part of whichconstitutes an insert. Referring to FIG. 8 a first portion of themagnetic bearing 364 is substantially encapsulated by being insertmolded into the body 314 at a position above the stator 320. A secondopposing portion of the magnetic bearing 366 is attached to the hub of aflange portion 368 of the disc support member 312. The second portion ofthe magnetic bearing 366 is attached to the flange portion 368 by glue.The first magnetic bearing portion 364 and the second magnetic bearingportion 366 are used in conjunction with a hydrodynamic bearing tocreate a working gap inside the hydrodynamic bearing 318 so that thereis no wear from start up conditions. The body 314 can be molded or thebody and/or magnet later machined to provide precise tolerance betweenthe first and second portions of the magnetic bearing. An advantage ofthe present invention is obtained by the fact that the first portion ofthe magnetic bearing is substantially encapsulated by the plastic of thebody. The first portion may initially be completely encapsulated and thebody machined to expose a surface of the magnet. Encapsulating the firstportion 364 facilitates machining of the magnetic bearings and thecleaning of any magnetic debris generated by such machining. The fourthembodiment may be made and used in a similar manner as the firstembodiment. This embodiment has the advantages discussed above inconjunction with the first embodiment as well as the advantage thatcomes from using a magnetic bearing.

Fifth Embodiment

Referring to FIG. 9, a fifth embodiment of the spindle motor 410 isshown. The fifth embodiment includes components that are similar to theprevious embodiments, in particular to the first embodiment. Amonolithic body 414 is formed using an encapsulation method. The primarydifference between the fifth embodiment and the first embodiment is thatthe fifth embodiment also includes an insert 468. The insert 468 ispreferably annular shaped and is positioned in between the bearings 418and the interior portion 430 of the body 414. The insert 468 isencapsulated at the same time as the stator 420 and the plastic tightlyretains and precisely positions the insert 468 relative to the stator.The insert 468 is preferably made of stainless steel. The insert 468serves to increase the overall strength and stiffness of the body 414.Also, the insert 468 improves the thermal conductivity of the body 414.It also eliminates differences in CLTE with the bearing materials. Italso is easier to glue to the steel bearing materials (gluing similarmaterials is easier than dissimilar materials). Additional inserts, suchas the base insert discussed above, could be added in this embodiment.The fifth embodiment may be made and used in a manner similar to thefirst embodiment. This embodiment has the advantages discussed above inconjunction with the first and third embodiments.

Sixth Embodiment

Referring to FIG. 10, a sixth embodiment of the spindle motor 510 isshown. A monolithic body 514 is formed using an encapsulation method.This embodiment includes components that are similar to those shown inprevious embodiments, in particular to the first embodiment. However,instead of having a shaft 16 that is attached with the disc supportmember 12 and rotates along therewith, like the first embodiment, thesixth embodiment has a shaft 516 that is fixed relative to thethermoplastic body 514 and hence is fixed relative to the statorassembly. The bearing 518 is located intermediate the disc supportmember 512 and the shaft 516. The disc support member 512 includes aninner portion 513 and an outer portion 515. The inner portion 513 isconcentrically disposed between the interior portion 530 of the body 514and the bearings 518. In operation, the bearings generally ride alongthe inner portion 513 of the disc support member 512 and the fixed shaft516 does not move with respect to the body 514. In this embodiment theshaft 516 may be lengthened so that it can be fixed to the hard discdrive case (not shown). This configuration serves to provide increasedmotor stiffness and to simplify construction of the hub and assemblyinto the motor. Comparing the first and sixth embodiments, it can beseen that in the present invention either the shaft or the bearing canbe fixed to the stator assembly, and the other of the shaft and bearingcan be fixed to the rotatable hub. In the first embodiment the bearingis fixed to the stator assembly. In the sixth embodiment the shaft isfixed to the stator assembly, preferably by being molded with the statorin the body.

The sixth embodiment may be made in a similar manner as the firstembodiment, except that the shaft may be included in the mold with thestator, or can be attached to the body 514 later. This embodiment hasthe advantages discussed above in conjunction with the first embodiment.

Seventh Embodiment

Referring to FIG. 11, a seventh embodiment of the spindle motor 610 isshown. This embodiment includes similar components as the previousembodiments and in particular to the first embodiment. A monolithic body614 is formed using an encapsulation method. The primary differencebetween this embodiment and the first embodiment is that the bearings618 are spaced a substantially greater distance apart from the shaft 616than the bearings 18 in the first embodiment. This spacing is achievedusing an upper insert 670 and a lower insert 672 substantiallyencapsulated by the body 614 (FIG. 12). These inserts are preferablyannular shaped, and act as extensions of the shaft 616. The upper insert670 and the lower insert 672 are preferably made of aluminum. The upperinsert 670 and the lower insert 672 are positioned between the bearings618 and the shaft 616. The bearings are then attached by glue. In thisembodiment, the shaft 616 is fixed to the body 614, partially by beingfixed to the inserts. The shaft extends from the base 622 so that it canbe fixed to the base of the hard disc drive. The seventh embodiment maybe made and used in a similar manner as the first embodiment. Thisembodiment has the advantages discussed above in conjunction with thefirst embodiment. An additional advantage of this embodiment is thatoversized bearings (having an outer diameter greater than 13 mm) may beused. These larger bearings generally have a longer life and can be runat higher speeds for longer periods of time. These larger bearings moreeffectively dissipate heat from the bearing surface.

Another major advantage of this embodiment stems from the lower bearingbeing positioned on the lower section of the hub. This arrangementdramatically increases stiffness and reduces disc wobble duringrotation. This in turn allows the use of enhanced data track density.The inserts 670 and 672 also provide stiffness and are thermallyconductive to dissipate heat.

Another advantage is that the manufacturing process to make the hubshown in this embodiment is significantly less complex and costly. Thehub is made from steel instead of aluminum, which eliminates the needfor a separate flux return ring. In essence the sidewall of the hubwhere the magnet 628 is attached act as the flux return ring.

In a less preferred embodiment of FIG. 11, instead of using the lowerinsert 672, the oversized lower bearing 618 could be supported by justhaving the body 614 of a large diameter at that point. In that instancethe body would be acting as an extension of the shaft. Alternatively, ashaft could be created that had one large flange on one end used tosupport the oversized bearing, and then the stator core lamination couldbe placed over the rest of the shaft and an insert like top insert 670fixed to the top of the shaft, and all of this structure placed in amold to encapsulate the stator and shaft.

Eighth Embodiment

An eighth embodiment of the spindle motor is shown in FIG. 13. Thisembodiment, referred to as a pancake motor, includes a monolithic body714 formed from an encapsulation method. The monolithic bodysubstantially encapsulates a circuit board 721. Copper traces (notshown) are placed on the circuit board and serve as the conductors thatcreate a plurality of magnetic fields. However, no steel core is used inthis type of stator. An IC chip controls current through these coppertraces. Passing current through the traces generates magnetic fieldswhich cooperate with fields in permanent magnet 728 attached to a discsupport member 712 to rotate the permanent magnet 728 and thereby rotatethe disc support member 712. This embodiment has the advantagesdiscussed above in conjunction with the first embodiment. The circuitboard is preferably a multilevel circuit board.

Ninth Embodiment

A ninth embodiment of the spindle motor 810 is shown in FIG. 14. Thisembodiment is somewhat similar to the first embodiment. A monolithicbody 814 is formed using an encapsulation method. The primary differencebetween the ninth and first embodiments is that in the ninth embodimenta magnet 828 is not fixed to the hub 812. Instead, the magnet 828 isdisposed around the shaft 816 and press fit, glued or welded and extendssubstantially along the length of the shaft. Further in this embodiment,the stator 820 contains a greater number of laminations. In addition,the body 814 is monolithic and contains an upper support portion 842 anda lower support portion 844 that are adjacent the upper bearing 846 andthe lower bearing respectfully 848. Further, the shaft 816 is attachedto the hub 812.

In this embodiment, the shaft 816 acts as the flux return for the magnet828. While not shown, it should be apparent that the present inventionis applicable to yet other embodiments of high speed motors. When thestator is energized, it causes the permanent magnet and shaft to rotate,which in turn causes the hub to rotate. In this embodiment the magnet isconnected to the hub by being fixed to the shaft which in turn is fixedto the hub.

Tenth Embodiment

A tenth embodiment, another pancake motor and a variation of the eighthembodiment, is shown in part in FIG. 17. This embodiment uses conductorsof copper wire shaped in the form of coils 922 placed upon the circuitboard 921, instead of copper traces. The magnet 928 is fixed to thebottom of the hub 912, but is shown in exploded form to facilitateillustration. Thermoplastic material is used to encapsulate the circuitboard and form body 914. Bearings (not shown) can be fixed to the body914.

Eleventh Embodiment

An eleventh embodiment of a motor 1010 of the present invention uses astator and shaft that are connected together by the phase changematerial, as shown in FIG. 18. The windings 1022 and remainder of stator1020 are encapsulated, and the phase change material also encapsulates acentral portion of the shaft 1016. The bearing 1018 is then attached toan exposed top portion of the shaft. The bottom portion of the shaftextends below the stator so that it can be attached to the base of thehard disc drive. The shaft is thus used as the mounting structure tohold the motor 1010 to the hard disc drive housing. The hub 1012includes a magnet 1028. One of the advantages of this embodiment is thatthe alignment between the shaft 1016 and stator 1020 can be set by thephase change material, and the shaft does not have to be separatelyglued in place.

Twelfth Embodiment

A twelfth embodiment of the invention is a hard disc drive 1102 shown inFIGS. 19 and 20. The motors of the previous embodiment were designed tobe manufactured separately and attached to the base or other housingcomponents of a hard disc drive. In this embodiment, the base 1134 ofthe hard disc drive is made as part of an assembly that alsosubstantially encapsulates the stator 1120.

The stator 1120 with windings 1122 and shaft 1116 (FIG. 19) arepreferably included into the base assembly 1134 (FIG. 20) when the bodyof phase change material is formed, such as by injection molding. Ofcourse, the shaft 1116 could be added to the base assembly afterwards.Preferably, the body of phase change material is a monolithic body ofthermoplastic material. The base assembly also preferably includes asecond shaft 1126 supported by the body of phase change material. Thissecond shaft 1126 is used to support the read/write head 1124 inoperable proximity to one or more discs 1114 supported on hub 1112. Thehub 1112 has a magnet 1128 connected thereto which is located inoperable proximity to the stator 1120 when the hub is rotatablysupported by bearing 1118 on shaft 1116. The hard disc drive 1102preferably includes other components, such as a circuit board 1130,wiring, etc. that is commonly used in hard disc drives and therefore notfurther described. Of course, a cover 1132 is preferably included andattached to the base assembly by conventional methods. The cover and thebase assembly cooperate to form a housing for the hard disc drive 1102.

One advantage of this embodiment of the invention is that the motor isbuilt directly onto the base assembly, reducing the number of parts.Further, the other components of the hard disc drive can be aligned withthe motor and disc or discs supported thereon.

Method of Developing a High Speed Motor

The present invention is also directed to a method of developing a highspeed motor. In an exemplary embodiment the high speed motor includes astator having conductors and the stator is substantially encapsulated ina body of phase change material. It has been found that using this basicdesign concept, high speed motors can be developed and quickly optimizedto meet various applications. Also, it has been found that when themotors include inserts, the development process includes another degreeof freedom in design. There are several basic design parameters that canbe varied when developing a motor according to the present invention: a)the composition (and thus characteristics) of the phase change material;b) the configuration of the body of phase change material; c) the useand dimensions and stiffness properties of inserts; d) the magneticdesign of the motor (the windings, core shape, etc.); and e) the shape,size and configuration of the hub (and any discs used thereon when themotor is for a hard drive).

In a first embodiment, where a motor is developed for a hard disc drive,the method includes the following steps: a) providing a stator havingmultiple conductors that create a plurality of magnetic fields whenelectrical current is conducted through the conductors, the stator beingsubstantially encapsulated within a body of first phase change material;b) assembling the stator with a bearing, shaft, hub and discs toconstruct a disc drive; c) energizing the stator and rotating the huband discs in a manner that generates vibrations, and measuring thefrequency of the vibrations; d) designing a second phase change materialthat dampens the vibrations generated by energizing the stator in stepc); and e) repeating steps a)-c), substituting the second phase changematerial for the first phase change material. At least one of the flexmodulus, elongation and surface hardness properties of the phase changematerial will be adjusted between the first and second phase changematerials to optimize vibration dampening. The phase change material ispreferably a thermoplastic. The advantages of this method of developinga high speed motor is that the above-identified properties of theplastic may be adjusted to meet the vibration dampening needs of avariety of different motor types and configurations. The reducedvibration will improve motor performance and can reduce audible noisegeneration.

It is also possible to change the configuration of the body so that itwill result in reduced harmonic oscillations and thus vibrations. Inthis embodiment, the method includes the steps of a) providing a statorhaving multiple conductors that create a plurality of magnetic fieldswhen electrical current is conducted through the conductors, the statorbeing substantially encapsulated within a body of phase change materialhaving a first configuration; b) assembling the stator with a bearing,shaft, hub and discs to construct a disc drive; c) energizing the statorand rotating the hub and discs in a manner that generates vibrations,and measuring the frequency of the vibrations; and d) reconfiguring theshape of the phase change material to a second configuration andrepeating steps a)-c), substituting the phase change material having thesecond configuration for the phase change material having the firstconfiguration. In this embodiment, the configuration of the body ofphase change material is adjusted to optimize vibration dampening. Wherethe body has a bore, a wall thickness and a flange as shown in FIGS. 5,7 and 8, the bore length, wall thickness and flange width are designparameters that can be modified between the first and secondconfigurations. Of course, other dimensions of body components can alsobe used. In this aspect of the invention, reconfiguring the shape of thephase change material would also include adding such elements as aflange, grooves, etc., or even adopting a relatively different overallshape.

When a stator assembly is designed that has phase change materialencapsulating the conductors, it is also possible to incorporate metalinserts into the stator assembly, and the shape, size or stiffness ofthose inserts can be selected and/or designed so as to dampen unwantedharmonics. In this embodiment, the method of developing a high speedmotor uses the steps of a) providing a stator having multiple conductorsthat create a plurality of magnetic fields when electrical current isconducted through the conductors, the stator being substantiallyencapsulated within a body of phase change material; b) assembling thestator with a bearing, shaft, hub and discs to construct a disc drive;c) energizing the stator and rotating the hub and discs in a manner thatgenerates vibrations, and measuring the frequency of the vibrations; d)including a metal insert substantially encapsulated within the body ofphase change material; e) repeating steps a)-d) and adjusting at leastone of the stiffness and thickness of the insert so as to optimizevibration dampening.

Another embodiment of the invention of developing high speed motorinvolves the steps of a) providing a stator having multiple conductorsthat create a plurality of magnetic fields when electrical current isconducted through the conductors, the stator being substantiallyencapsulated within a body of phase change material; b) assembling thestator with a bearing, shaft, hub and discs to construct a disc drive;c) energizing the stator and rotating the hub and discs in a manner thatgenerates vibrations, and measuring the frequency of the vibrations; andd) modifying of the hub, the discs or both so that the disc drive hasvibrations at frequencies of harmonic oscillation that are dampened bythe phase change material.

Of course combinations of these four methods may also be used, such asvarying both the characteristics of the phase change material and addingan insert to the body. Also, if the motor is to be used in a deviceother than a hard disc drive, it can be developed in the same manner,except that a gear, pulley, rim, fan blade or whatever other componentis to be turned by the motor can be put on the motor instead of the huband discs before the motor is energized.

The present invention is also directed to an alternative method ofdeveloping a high speed motor. Like the other methods, this method alsoinvolves a high speed motor that includes a body that is comprised of aphase change material that substantially encapsulates a stator. The highspeed motor includes one or more, and generally a plurality of solidparts to be used in the motor either near or within the body, such asbearings and inserts. In addition, there are solid parts that are nearthe body, such as a disc support member and a hard disc drive base. Themethod of developing the high speed motor comprises designing a phasechange material to have a coefficient of linear thermal expansion suchthat the phase change material contracts and expands at approximatelythe same rate as the one or more solid parts. For example, the preferredphase change material should have a CLTE of between 70% and 130% of theCLTE of the core of the stator. The phase change material should have aCLTE that is intermediate the maximum and minimum CLTE of the solidparts where the body is in contact with different materials. Also, theCLTE's of the body and solid part(s) should match throughout thetemperature range of the motor during its operation. An advantage ofthis method is that a more accurate tolerance may be achieved betweenthe body and the solid parts because the CLTE of the body matches theCLTE of the solid parts more closely.

Most often the solid parts will be metal, and most frequently steel,copper and aluminum. The solid parts could also include ceramics. Inalmost all motors there will be metal bearings. Thus a common element ofthis aspect of the invention is developing a motor by designing thephase change material to have a CLTE approximately the same as that ofthe metal used to make the bearings.

Most thermoplastic materials have a relatively high CLTE. Somethermoplastic materials may have a CLTE at low temperatures that issimilar to the CLTE of metal. However, at higher temperatures the CLTEdoes not match that of the metal. A preferred thermoplastic materialwill have a CLTE of less than 2×10⁻⁵ in/in ° F., more preferably lessthan 1.5×10⁻⁵ in/in ° F., throughout the expected operating temperatureof the motor, and preferably throughout the range of 0-250° F. Mostpreferably, the CLTE will be between about 0.8×10⁻⁵ in/in ° F. and about1.2×10⁻⁵ in/in ° F. throughout the range of 0-250° F. (When the measuredCLTE of a material depends on the direction of measurement, the relevantCLTE for purposes of defining the present invention is the CLTE in thedirection in which the CLTE is lowest.)

The CLTE of common solid parts used in a motor are as follows:

23° C. 250° F. Steel 0.5 0.8 (×10⁻⁵ in/in ° F.) Aluminum 0.8 1.4 Ceramic0.3 0.4

Of course, if the motor is designed with two or more different solids,such as steel and aluminum components, the CLTE of the phase changematerial would preferably be one that was intermediate the maximum CLTEand the minimum CLTE of the different solids, such as 0.65 in/in ° F. atroom temperature and 1.1×10⁻⁵ in/in ° F. at 250° F.

One preferred thermoplastic material, Konduit OTF-212-11, was made intoa thermoplastic body and tested for its coefficient of linear thermalexpansion by a standard ASTM test method. It was found to have a CLTE inthe range of −30 to 30° C. of 1.09×10⁻⁵ in/in ° F. in the X directionand 1.26×10⁻⁵ in/in ° F. in both the Y and Z directions, and a CLTE inthe range of 100 to 240° C. of 1.28×10⁻⁵ in/in ° F. in the X directionand 3.16×10⁻⁵ in/in ° F. in both the Y and Z directions. (Hence, therelevant CLTEs for purposes of defining the invention are 1.09×10⁻⁵in/in ° F. and 1.28×10⁻⁵ in/in ° F.) Another similar material, KonduitPDX -0-988, was found to have a CLTE in the range of −30 to 30° C. of1.1×10⁻⁵ in/in ° F. in the X direction and 1.46×10⁻⁵ in/in ° F. in boththe Y and Z directions, and a CLTE in the range of 100 to 240° C. of1.16×10⁻⁵ in/in ° F. in the X direction and 3.4×10⁻⁵ in/in ° F. in boththe Y and Z directions. By contrast, a PBS type polymer, (Fortron 4665)was likewise tested. While it had a low CLTE in the range of −30 to 30°C. (1.05×10⁻⁵ in/in ° F. in the X direction and 1.33×10⁻⁵ in/in ° F. inboth the Y and Z directions), it had a much higher CLTE in the range of100 to 240° C. (1.94×10⁻⁵ in/in ° F. in the X direction and 4.17×10⁻⁵in/in ° F. in both the Y and Z directions).

In addition to having a desirable CLTE, the preferred phase changematerial will also have a high thermal conductivity. A preferredthermoplastic material will have a thermal conductivity of at least 0.7watts/meter° K. using ASTM test procedure 0149 and tested at roomtemperature (23° C.).

Stator assemblies with a body of phase change material partiallyencapsulating the stator wherein the phase change material has the CLTEor thermal conductivity as described above are themselves novel anddefine another aspect of the present invention. Once encapsulated, thestator assembly will preferably be able to meet disc drivemanufacturers' industry standards for particulate emission, requiringthat when tested the parts will produce 10 or fewer particles of 0.3micron and larger per cubic foot of air. This is primarily becausemachined mounting plates are eliminated and other sources ofparticulates (steel laminations, wound wire and wire/terminalconnections) are sealed in the encapsulation.

Also, the encapsulation reduces outgassing because varnish used toinsulate wire in the windings and epoxy used to prevent steellaminations from oxidizing are hermetically sealed inside the statorassembly. Also, with fewer parts there is less glue needed to hold partstogether. This reduced outgassing reduces the amount of material thatcould effect the magnetic media or heads used in the disc drive.

Another aspect of the invention utilizes the basic motor described abovethat has dampened vibrations to make a hard disc drive. The dampenedvibrations can be either in the audible frequency range, thus resultingin a disc drive with less audible noise, or in other frequencies. Asmentioned earlier, the degree to which data can be packed onto a harddrive is dependent on how close the data tracks are spaced. Due toreduced vibrations resulting from aspects of the present invention, thedata tracks can be more closely spaced and the hard drive stilloperated.

The vibrations of concern are generally produced by harmonicoscillations. The phase change material can be selected so as to dampenoscillations at the harmonic frequency generated by operation of themotor, many of which are dependent on the configuration of the windingsor other conductors. Thus, in one aspect, the invention is a motor anddisc assembly wherein the motor comprises a stator having multipleconductors that create a plurality of magnetic fields when electricalcurrent is conducted through the conductors and a monolithic body ofphase change material substantially encapsulating the conductors. Inthis respect, the phase change material has a vibration dampening effectso that the motor and disc assembly has a reduction of harmonicoscillations.

There are a number of properties of the phase change material that canbe varied in a way that will allow the phase change material to dampendifferent harmonic frequencies. This includes adding or varying theamount of glass, Kevlar, carbon or other fibers in the material; addingor varying the amount of ceramic filler in the material; changing thetype of material, such as from polyphenyl sulfide to nylon or otherliquid crystal polymers or aromatic polyesters, adding or graftingelastomers into a polymer used as the phase change material; and using adifferent molecular weight when the phase change material is a polymer.Any change that affects the flex modulus, elongation or surface hardnessproperties of the phase change material will also affect its vibrationdampening characteristics.

One way to determine the effectiveness of vibration dampening, and thusto select a suitable material, is to make up motor configurations wheredifferent phase change materials are used, and then measure thevibration dampening accomplished by each material. The vibrationdampening can be measured with a capacitance probe or laser Dopplervibrometer. In the range of 200-2000 Hz, and preferably in the range of300-2000 Hz, the disc drives using high speed motors of the presentinvention will preferably have an amplitude decrease of harmonicvibration of at least 5 and more preferably at least 10 decibels. In theaudible range, 20-15,000 Hz, the dampening will preferably be at least2, more preferably at least 5 decibels in reduction in harmonicfrequency amplitude. These reductions are assessed based on a comparisonof the vibrations of the same motor but without the stator beingencapsulated.

The reduced vibrations thus allow for a unique hard disc drive with highdata density and method of manufacturing the same. In this aspect of theinvention, a spindle motor is constructed with reduced vibrationcharacteristics. The motor includes a stator assembly with a statorsubstantially encapsulated in a body of phase change material, arotatable disc support member having a magnet connected thereto, ashaft, a bearing surrounding the shaft and either the shaft or bearingbeing fixed to the stator assembly and the other of the shaft or bearingbeing fixed to the disc support member. The spindle motor is built intoa hard disc drive with a magnetic storage media on the disc support. Thereduced vibration characteristics of the motor is taken advantage of byhaving close data tracks on the magnetic storage media. Preferably thedata tracks are spaced so as to have at least 10,000 tracks/inch.

The vibration dampening ability of the phase change material may also beused in another aspect of the invention, a hard disc drive having a highspeed spindle motor with improved shock resistance. In this aspect ofthe invention, the body of phase change material is shock absorbing andis attached to the housing of a hard disc drive. The vibration dampeningminimizes the transfer of energy between the housing of a hard discdrive and the magnetic storage media.

One difficulty encountered in hard disc drive manufacturing is that thevarious components used to make the motor often have particulates thatmust be ultrasonically cleaned off of the parts before they areassembled, and thereafter the assembly operation has to be carried outin a clean room environment. For example, when a stator is made, thesteel core pieces that are laminated together and the wire used to makethe windings are prone to have small particulates associated with themthat must be removed. The particles are removed from the laminationsbefore the windings are applied, because expensive and time consumingcleaning techniques would be required to clean the stator after it wasbuilt if the parts were not pre-cleaned. Even then, as the motor isassembled, it is possible for varnish on the windings to come off, orother particles to be generated when pieces of the motor strike oneanother.

One of the aspects of the invention takes advantage of the eliminationof these particles when the stator is encapsulated and the fact that theencapsulation makes the stator assembly durable so that low costultrasonic cleaning can be used. First, the stator laminations andwindings do not need to be cleaned before they are encapsulated.Thereafter, once the stator assembly has been made and cleaned, it canbe used to construct a hard disc drive without the need for a clean roomenvironment. Thus, in this aspect, the invention involves the followingsteps: a) constructing a stator made of a laminated steel core and wirewindings; b) substantially encapsulating the stator in a body of phasechange material to form a stator assembly; c) ultrasonically cleaningthe stator assembly; d) constructing the stator assembly with a bearing,shaft and hub to form a spindle motor; and e) constructing the spindlemotor into a hard disc drive.

One unique aspect of the invention is that a variety of stators can beencapsulated in the same mold tool. For example, stators that vary withrespect to one or more of their properties, such as their number ofturns of wire, their number of poles, their diameter and/or theirthickness, may still all fit within the same mold tool. As a result, afirst variety of stator can be encapsulated by injection molding orotherwise adding a thermoplastic or other phase change material to themold tool, and then using the first variety of stator, a bearing and ashaft to build a first variety of motor. Then, a second variety ofstator can be encapsulated and used to build a second variety of motorusing the same or different bearings and shaft. Not only does thisreduce the number of mold tools that are needed, but the statorassemblies will have a final uniform size and shape, since the phasechange material body will have the same dimensions for each. As aresult, other components of the motor and the disc drives in which theyare used, such as the housing, can be constant between different discdrives.

In addition to the above discussed embodiments, a similar structure,method of manufacture and method of developing a high speed motor can beemployed in high speed motors used in other types of applications. Forexample, these high-speed motors could be used in CD, DVD players,videocassette systems, digital cameras and in robotic servomotors.

Following is a summary of some of the benefits of preferred embodimentsof the invention.

The reduced vibration resulting from encapsulation of the stator,especially with a thermoplastic material that is designed to reducevibration for a specific motor configuration, is beneficial in a numberof respects. First, the hard disc can be designed to pack data moreclosely together. Preferably the hard disc drive will use data trackscompact enough that 10,000 data tracks per inch can be reliablyaccessed. With reduced vibration it is practical to use hydrodynamicbearings.

Also, with reduced vibration, there will be less friction and wear inthe bearings, which results in less heat being generated by the motor,in turn resulting in longer motor and bearing life and more power fromthe motor. Utilizing aspects of the present invention it is possible toconstruct motors able to spin in hard disc drives at speeds over 5,000rpm. A preferred motor will be able to spin at 7,500 rpm or greater, anda more preferred embodiment will be able to spin at 10,000 rpm orgreater.

The present invention can be used with motors having laminated cores andwire windings. It can also be used on motors using a circuit boardconfiguration or coils on a circuit board.

A number of ways to improve thermal conductivity are presented. First,the phase change material will itself provide some heat dissipation.Second, the phase change material can include additives that willenhance its thermal conductivity. Third, heat conductive inserts can beincluded in the motor. Fourth, the body of phase change material, bybeing in contact with a number of parts of the motor and/or disc drive,can act as a pathway for heat such that those other parts of the motorand/or disc drive can act as heat sinks. This improved thermalconductivity provides longer life to the electrical and bearingcomponents of the motor, a higher power device, higher efficiency andlower current draw. If the motor is in a battery powered device, thiswill extend the battery life.

The invention makes it practical to use oversized bearings, whichresults in less vibration induced wear and lower temperature, as well aslonger bearing life.

The unique motor design allows for unique manufacturing possibilities.The laminations and windings do not need to be separately cleaned and,once the stator assembly has been encapsulated, it will not generatecontaminants. In addition, if inserts are encapsulated and then machinedto provide precise dimensions, one cleaning step can be used after allfabrication steps. It is not practical to do this type of machining onassembled parts without the present invention because there is nopractical way to clean the entire assembly after such a machiningoperation. Thus, hard disc drives can be constructed without the needfor stringent “clean room” conditions. Only one ultrasonic cleaning stepwill be required. Cellular manufacturing technology can be used. Themotor can be made anywhere and then cleaned just before being assembledwith the hard drive. There is no need for costly packaging to keep thestator assembly clean. Also, the durability of the stator assemblyallows for low cost shipping.

Hard drives built with the preferred motors will have better reliabilityfrom lower particulate levels and reduced outgassing. The hard driveswill have improved shock resistance if the drive is dropped. The headsused in the hard disc drive are electrically isolated from theconductors in the motors without the need for a separate insulator. Thepreferred motors and disc drives will have quieter operation.

The use of an encapsulated stator allows the terminal connectors to beintegrated into the body. In general, the motor can be more easilyassembled and will include fewer parts. As noted above, the stack-uptolerances are reduced because the phase change material can be designedwith a CLTE that closely approximates that of other motor components. Bymatching CLTE, one also obtains better environmental conditions.Otherwise, plastics get microcracks and moisture or other fluids canattack the encapsulated components.

There are a number of cost benefits associated with aspects of thepresent invention. There are cost benefits from fewer components. Thedie cast aluminum base 2 (see FIG. 1) and various insulators arereplaced with one body of phase change material. The manufacturingprocess has reduced costs. Tools used to injection mold thermoplasticshave a longer tool life than those used in die casting. There are lowercosts because plastic molding tools produce more parts per hour thanaluminum die casting tools. There are also lower costs because plasticparts require less post mold machining than aluminum parts.

There are also benefits associated with development time and cost fornew motor configurations. Design implementation can be faster. First,since there are fewer parts, less parts have to be designed for each newmotor. Second, fewer tools are needed, since fewer parts are required.Third, injection molding tools are modular in nature. This allowstooling to be easily customized without requiring a redesign of thewhole tool. In many cases, one tool can be used for multiple productdesigns and iterations. For example, plastic molding tools might be ableto be used with multiple winding configurations.

While the embodiments of the invention disclosed herein are presentlyconsidered to be preferred, various changes and modifications can bemade without departing from the spirit and scope of the invention. Thescope of the invention is indicated in the appended claims, and allchanges that come within the meaning and range of equivalents areintended to be embraced therein.

What is claimed is:
 1. A stator assembly comprising a) a magneticallyinducible core having a plurality of salient poles; b) a plurality ofconductors comprising wire windings around said poles such that magneticfields are induced in the core when electrical current is conductedthrough the conductors; and c) a body of a phase change materialsubstantially encapsulating the core and the conductors, the phasechange material having a coefficient of linear thermal expansion ofbetween about 0.8×10⁻⁵ in/in ° F. and about 1.5×10⁻⁵ in/in ° F.throughout the range of 0-250° F.
 2. The stator assembly of claim 1wherein the phase change material has a coefficient of thermalconductivity of at least 0.7 watts/meter° K. at 23° C.
 3. The statorassembly of claim 1 further comprising terminals for connecting theconductors to a power source, the terminals being partially encapsulatedin the body.
 4. The stator assembly of claim 1 further comprising one ormore metal inserts molded into the body, the inserts providing one ormore properties selected from the group consisting of increasedrigidity, increased thermal conductivity, vibration dampening andenhanced magnetic effect.
 5. The stator assembly of claim 1 wherein thecore is made from steel laminations.
 6. The stator assembly of claim 1wherein the salient poles are directed outwardly.
 7. The stator assemblyof claim 1 wherein the salient poles are directed inwardly.
 8. Thestator of claim 1 wherein the phase change material includes ceramicparticles.
 9. The stator of claim 1 wherein the phase change materialcomprises polyphenyl sulfide.
 10. A motor comprising the stator assemblyof claim
 1. 11. A stator assembly comprising: a) a stator having amagnetically inducible core with salient poles and multiple conductorsthat create a plurality of magnetic fields when electrical current isconducted through the conductors; and b) a body of phase change materialsubstantially encapsulating the core and the conductors, the phasechange material having a coefficient of linear thermal expansion ofbetween about 0.8×10⁻⁵ in/in °F. and about 1.5×10⁻⁵ in/in °F. throughoutthe range of 0-250° F., a thermal conductivity of at least 0.7watts/meter °K. and a dielectric strength of at least 250 volts/mil. 12.A stator assembly comprising: a) a stator having a core with salientpoles and multiple conductors that create a plurality of magnetic fieldswhen electrical current is conducted through the conductors; and b) abody of phase change material substantially encapsulating theconductors, the phase change material being an injection moldedthermoplastic having a coefficient of linear thermal expansion ofbetween about 0.8×10⁻⁵ in/in °F. and about 1.5×10⁻⁵ in/in °F. throughoutthe range of 0-250° F., a thermal conductivity of at least 0.7watts/meter° K. and a dielectric strength of at least 250 volts/mil.